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Mach Discussion => General Mach Discussion => Topic started by: dresda on April 18, 2009, 12:14:53 AM

Title: What size motors?
Post by: dresda on April 18, 2009, 12:14:53 AM
Hi, can somebody tell me what size motors I should use for a standard Bridgeport size mill.
Steppers or sevos, should the steppers be Nema 34 and around 1000oz-inch?
4-6-8 wire? How many ppr? Bi-polar or?
This is all new to me, only ever worked with Ac servo's and Fanuc, but now going over to the dark side with mach3... :-\
Ray.
Title: Re: What size motors?
Post by: simpson36 on April 18, 2009, 05:09:14 AM
Take a read on the www.geckodrives.com site. Lots of good info and formulai

Make sure you do your own price checking in whatever you are considering. Also note the dates on any forum postings you pick up with a search engine.

I can't tell you how many times I read about servos being 2 or more times as expensive as steppers. My own research into pricing showed a $15 difference per axis. Insignificant.

As a newbee, I followed the advice de jour and went with steppers, albeit the most powerfull I could get in NEMA 23. Steppers make sense in some applications, but if I had it to do over . . . . 

My new servo motor should be here shortly and I will take a walk down that path in preparation for retrofitting another larger mill.

Title: Re: What size motors?
Post by: BClemens on April 18, 2009, 06:52:09 AM
There are benefits and pitfalls with both type drive motors. Servos are more powerful at higher speeds where steppers begin to decline but the most prevalent benefit to stepper motors is that they don't require tuning via their drive. Tuning can be a problem then it must be done at a later date with servo motors again - and again. I would direct drive that Bridgeport with about 1500 Oz In stepper motors with appropriate drives from Gecko and forget about -  tuning, belt adjustments and wear, and all the 'bracketry' required for servo motors and their belt reduction and adjustment fixtures. I converted a similar mill and used servo motors.....And BTW: servo motors are very much more expensive than equivalent stepper motors and servo motors require an encoder to give position feedback to the drive where steppers are where they are told to be. Use size 34's.



2.25 cents worth at least!

Bill C.
Title: Re: What size motors?
Post by: HimyKabibble on April 18, 2009, 11:30:22 AM
There are benefits and pitfalls with both type drive motors. Servos are more powerful at higher speeds where steppers begin to decline but the most prevalent benefit to stepper motors is that they don't require tuning via their drive. Tuning can be a problem then it must be done at a later date with servo motors again - and again. I would direct drive that Bridgeport with about 1500 Oz In stepper motors with appropriate drives from Gecko and forget about -  tuning, belt adjustments and wear, and all the 'bracketry' required for servo motors and their belt reduction and adjustment fixtures. I converted a similar mill and used servo motors.....And BTW: servo motors are very much more expensive than equivalent stepper motors and servo motors require an encoder to give position feedback to the drive where steppers are where they are told to be. Use size 34's.



2.25 cents worth at least!

Bill C.

"servo motors are very much more expensive than equivalent stepper motors" - That is simply not true!  The difference is perhaps very, very, very worst case $100 more per axis, which is almost lost in the noise compared to the overall cost of a decent conversion on a knee mill.  And the difference in performance can be very significant indeed.  There are plenty of valid reasons for preferring steppers over servos in some applications, but cost is not one of them, unless you're really pinching pennies.

I used 850 oz-in servos from www.homeshopcnc.com, with 2.5:1 GT2 belt reducers, and Gecko G320s.  My machine can get up to 400 IPM rapids on X and Y, and it absolutely un-stoppable at machining speeds.  I've snapped off 1/2" endmills without losing position.  Try to get that kind of performance from steppers.

Regards,
Ray L.
Title: Re: What size motors?
Post by: Overloaded on April 18, 2009, 12:20:35 PM
Quote
I would direct drive that Bridgeport with about 1500 Oz In stepper motors with appropriate drives from Gecko and forget about -  tuning, belt adjustments and wear, and all the 'bracketry' required for servo motors and their belt reduction and adjustment fixtures.
Hi Bill,
  Can you NOT direct drive with servos ?  What is the limitation here ? Please explain.
Thanks,
RC
Title: Re: What size motors?
Post by: Hood on April 18, 2009, 12:33:22 PM
All depends what you want out of your machine, I have steppers on my Bridgeport and they work well, at the time I did that there was a BIG difference between servos and steppers because the cheap Chinese DC Servos were not readily available at that time.
 It works well and has never given me problems but it is slow, 2500mm/min rapids (100IPM) and accel is not lighning fast either but as I said it works well  and its fine if you are not in a real hurry.

 Never tried DC servos  with the likes of the Geckos so cant comment on them.

 On the Lathe and Beaver Mill I use AC Servos and they are blazingly fast both in rapids and accel but you need decent sized ones to do that, you could probably use 0.75 to 1Kw with some gearing but for me 1:1 gives the full benefits of the AC Servos so I have  1.5Kw on the Beaver axis  (bit bigger than a Bridgeport) and 7.5KW on the spindle, the lathe being a big machine needs 3KW on the axis and 12.5Kw on the spindle
 AC Servos are not cheap but the drives give you many more options than the standard  DC drives such as Geckos/Rutex etc.

All boils down to what you want out of your machine and how much you have to spend.

Hood
Title: Re: What size motors?
Post by: dresda on April 18, 2009, 01:57:39 PM
Thanks for the prompt replies. I have the mach3, have fanuc Ac servo's on the machine at the moment and  ordered DSPMC module from Vital systems but I would like to also try steppers or cheap servo's.
I am still  looking at Camsoft but can't justify the cost at the moment with the economy the way it is.
One big advantage for me with Camsoft is the fact that I don't have to learn VB or C++.
Ray.
Title: Re: What size motors?
Post by: Hood on April 18, 2009, 02:34:17 PM
If you have the Fanuc servos and you are getting the DSPMC then you are all set. As for needing to learn VB or C++ why would you need that? Custom macros require VB but will you need them?
Hood
Title: Re: What size motors?
Post by: BClemens on April 18, 2009, 04:00:40 PM
Should have qualified that statement about the price difference between good quality DC servo motors and stepper motors.... The DC servo motors that I used on this Bridgeport type machine are now about $600.00 each (with encoders) and similar sized (power wise) stepper motors are about a third of that. AC servo motors are probably worth checking out due to the increase in the price of DC motors - good quality.

Yes, servos motors can direct drive but low speed torque for a DC servo motor is probably about three times what a stepper requires - attempts to provide that low end torque have been in the form of spiral stacked armatures and the like which makes servo motors all the more expensive. The basic form in terms of manufacture of a stepper motor makes them cheaper than a servo motor as well - example - there are no brushes to contend with in a stepper. The small DC starters for outboard motors are a good example of the increase in price of that sort of DC motor - similar to servos for torque for size.

I'm generalizing by passing on my experiences with this. Didn't intend to ruffle any feathers. That seems easily done here....I guess I should just keep my experiences to myself, meaning that I'm not welcomed here?

Fine

Bill C.
Title: Re: What size motors?
Post by: Hood on April 18, 2009, 04:05:58 PM
Bill you are more than welcome here, if you ruffle feathers then so be it, just :)
Hood
Title: Re: What size motors?
Post by: Overloaded on April 18, 2009, 05:34:28 PM
Hey Bill,
   Not ruffled here.... just embarking on a similar build/retro and am a glutton for info, hence the question, NOT contradiction. I am planning on AC servos 1:1 belted.
Never saw a BP type direct coupled but see it's common on dinky mills. Seems it would be awkward.
Wasn't aware of the constant tuning either....thought that was a one time deal.  Bummer.
Thanks for your pennies,
RC

 
Title: Re: What size motors?
Post by: Hood on April 18, 2009, 05:38:30 PM
RC tuning is a one time thing, well if you get it right anyway ;D
Hood
Title: Re: What size motors?
Post by: budman68 on April 18, 2009, 05:49:13 PM
Quote
I'm generalizing by passing on my experiences with this. Didn't intend to ruffle any feathers. That seems easily done here....I guess I should just keep my experiences to myself, meaning that I'm not welcomed here?

Fine

Bill C.

Bill, don't ever feel that way, we're people and the internet is not the best way to get our points across sometimes. I can piss people off all day and I never meant a bit of it the way that it was taken. It's the loss of "inflection" that screws it up for us. It's too bad we can't all be in the same room at times, but of course, we may end up beating the crap out of each other too,  who knows,  :D

No worries here -  8)

Dave
Title: Re: What size motors?
Post by: BClemens on April 18, 2009, 06:45:49 PM
Ha ha, good term: "inflection"...

 So the next milling machine that I convert will have steam engines on it, but was wondering which to use - turbine or reciprocating? Doesn't really matter because I could snap a 4 inch end mill at will! And rapid travel....? I could over in to next week in a wink.   ;)

A commercially available NC mill is using direct drive series 34 stepper motors and they give reasons why. http://www.cncmasters.com/CNCMasters_Supra_ProductGuide.pdf

We are seriously looking at purchasing one of these...

 Thanks once again,
Bill C.
Title: Re: What size motors?
Post by: Overloaded on April 18, 2009, 07:06:54 PM
Dresda,
   Here is some info that may interest you.

http://geckodrive.com/support.aspx?q=10002

They have Coal fired, Wood fired and Nuclear. he he he

Bill,
   That's a neat looking little mill, first one I saw like that.
 Might consider that on mine.....thanks. Would be nice to eliminate the belt and pulleys, especially if it's 1:1 anyway.
RC
Title: Re: What size motors?
Post by: HimyKabibble on April 18, 2009, 08:29:26 PM
Ha ha, good term: "inflection"...

 So the next milling machine that I convert will have steam engines on it, but was wondering which to use - turbine or reciprocating? Doesn't really matter because I could snap a 4 inch end mill at will! And rapid travel....? I could over in to next week in a wink.   ;)

A commercially available NC mill is using direct drive series 34 stepper motors and they give reasons why. http://www.cncmasters.com/CNCMasters_Supra_ProductGuide.pdf

We are seriously looking at purchasing one of these...

 Thanks once again,
Bill C.

Probably a nice machine, but 50 IPM is a *painfully* slow max speed for a machine that size.  That's almost as full minute to go end-to-end on the X axis, and almost 20 seconds on Y.  The basic machine is identical to mine - same castings, same paint even.  It is a very good basic machine.

Regards,
Ray L.
Title: Re: What size motors?
Post by: dresda on April 18, 2009, 09:08:23 PM
Hood,
 I will have to learn VB for multi axis and tool changers etc.
ray.
Title: Re: What size motors?
Post by: Hood on April 19, 2009, 05:04:38 AM
dresda
 I dont really know VB but managed to write macros for the toolchanger, m3,m4,m5,spindle speed etc on my lathe, its not that hard but if you need help there are lots here that are good with VB so I am sure you will get all the help you need.
 I also used a PLC for the tooldhange on my lathe, depending on how yours operates it may be something you will need although possibly the DSPMC will provide enough I/O for you (dont know much about it)

Hood
Title: Re: What size motors?
Post by: simpson36 on April 19, 2009, 05:37:15 AM
What's better Ford or Chevy? That is an emotional or personal opinion type of debate and is therefor unresolvable. The debate betwen steppers vs servos will also be unresolvable so long as it is argued by fanboys instead of facts.

I have lost count of how many of these debates I have read and probably less than 10% of them have any facts whatsoever.

Servos are more expensive than steppers in the same way as a Corvette is more expensive that Ford Escort. It is frankly rediculous to compare those two cars based on price alone and make a blanket statement the they are both 'cars' and therefore the  Escort is 'just as good'

If your objective is to take your kid to school over surface streets at 35mph max, THEN there may be a valid argument there. If your objective is to autocross without building a race car from the ground up, then it matters zero how little the Escort costs because it is simply incapable of doing the job.

If one prices out, using CURRENT pricing, servo motors and the required encoder and driver and a stepper and required driver in cases where anything resembling  equivalent performce is a criteria, then steppers and DC servos are very comperable in price.

Exactly how does one go about comparing steppers and servos? I have seen people compare the torque, but that is a completely invalid comparison because the motors are rated differently and have vastly different charactaristics. Torque is a STATIC measure. That's not an opinion, that is a fact. Moving objects requires POWER. That is also a fact. POWER is about doing work over TIME, also fact. Torque  is ONE number in the equation. I did a comparison of stepper vs servo of similar 'rated' torque and posted it in this forum. I also posted the formulas used so anyone was free to discredit them. Nobody did.  The servo was many, many times more powerfull.

A Corvette motor has 500hp and a semi diesel has only 300, therefor a Corvette engine will perform better in a semi truck than a diesel. That is simply an uneducated statement and is the type of logic that often defends stepper motors.

I have to agree with whoever said that the stepper powered full size mill that was used as an example is pitifully slow. I would add that is is also pitifully weak.

Servo motors top out early in the power game and above that there is only a choice between DC servos and AC servos. A Ford Escort gets much better mileage than a semi, so putting a Ford escort engine into the semi would result in much better mileage for the semi. This is also the type of logic that defends steppers on big machines.

It is really like comparing a pickup truck and an earth mover and saying the pickup is 'just as good' because it also can move dirt from point A to point B and it is cheaper.

Flame suit *on*  >:D
Title: Re: What size motors?
Post by: BClemens on April 19, 2009, 06:37:13 AM
All well and good, but the USE of these two motors is what is specifically asked by the OP. While a servo motor is quietly absorbing 'inrush' current to begin to move - the stepper motor has already moved - more poles more power - simple. Once the servo motor takes enough current to overcome the load - then hands down the servo motor takes off and wins the challenge and can continue to climb in speed with the same 'power' that it required at the start then actually become more efficient. The stepper cannot keep up and becomes less efficient at speed. Most people know that already.

But, for slow, precise, powerful movement of a device that must be moved by controlled and accountable movements. The stepper wins. And I did say slow as well.

I'll take steam power. I also don't believe the OP was interested in all this super factual information - he was merely asking for opinions. If you like to poo poo others' opinions and experience, then you may require your flame suit but not for my account. Using the Ford Escort and Corvette as a parallel here is totally invalid and is a basic over simplification - although I always buy USA made products when available.

I read where you come off, as a rolling boulder of knowledge.

Bill C.


 
Title: Re: What size motors?
Post by: simpson36 on April 20, 2009, 05:43:13 AM
Bill;  Just FYI, I don't take myself all that seriously, nor do I get emotional over forum chatter. My 'opinions' are no better or worse than anyone elses, however facts are facts and I welcome any challenges in that regard.

I would like some clarification on one of your comments. You mentioned 'inrush of current' to a servo motor.

Sounds like you are implying that a servos is unpowered when not moving. If that is so, how does it have any holding power?

As to steam power, I think better to use a twelve year old kid on a hand crank.  . .  you have to feed them anyway, and it keeps them out of trouble . . . >:D
Title: Re: What size motors?
Post by: BClemens on April 20, 2009, 06:25:48 AM
Well, it takes time to build up a magnetic field, and more time in relation to the size of and wire size of the armature. DC Servo motors are basically two pole motors with a wound armature with brushes to provide the current path....one large winding contacted at each end with a carbon brush. Takes time to build that field compared to a motor with independent windings and multi pole - commonly three in a light duty stepper. The step magnetic field is built up much faster and the motor has reacted much faster - lighter windings and multi sources for multi magnetic fields.

The starting current or 'inrush current' is a factor with any electric motor - AC, DC, or universal. That current is usually a minimum of twice the running current. The larger the motor the more starting current required.

Now, as I had said earlier; while the DC servo motor is absorbing current into its one large winding to build a starting field, the stepper has done its job - one measured and very accurate step. Of course you would size a motor appropriately but size for size and load for load the time of reactance is very factually faster with a stepper motor. But to carry a load at speed - the servo motor is much more efficient.

Now if snapping endmills or rapid travel of a table is the prime interest, then a servo motor is the way to go. If machine work even on aluminum is the prime importance, then a stepper motor is very likely very adequate, sized for the job. Both types of motors have their place - it just depends on how much money and time one wishes to devote to either converting a machine or machining hardened 17-5 stainless steel. One is a given, the other is totally for practicality. To use one of your parallels: why use a high speed V-8 when a lugger four cylinder will do the job?

Serious? Hell yes I'm serious. Intelligence is wasted on a smart ass who demeans those around him. A true engineer is first taught how to be humble - otherwise his talents never enter a prototype shop where he must deal with those with different talents and sometimes a different outlook on life. I'll work with a good machinist with one leg and blind in one eye before I will sit down to converse with an engineer with his head up his ass.

Bill C.

Title: Re: What size motors?
Post by: Hood on April 20, 2009, 06:40:07 AM
Bill,
 where do AC servos (or DC Brushless) fall in relation to what you said above? From what I can see their construction is similar to steppers in that the coils are in the motor housing and the armatures have the magnets.
 I have some 4 pole, some 6 pole and mostly  8 pole AC Servos, any info on the difference between them with regards machine tools?
Hood
Title: Re: What size motors?
Post by: BClemens on April 20, 2009, 07:18:45 AM
Hood,

AC servo motors are the most efficient type for slow running and holding power because of their multi poles. The current does not differ with running or stationary (holding) since the major factor in their speed is frequency. They have a quiescent current value that is a factor in sizing a power source but again their speed is a function of the frequency of the applied current and also the number of poles. Yes, they are functionally very similar to a stepper motor so their reactance is very much faster than a DC servo motor.

An AC servo motor is basically in a locked rotor state for holding. The current maintains that state and is the design difference between them and a 'regular' AC motor which will heat up from its own magnetic feedback. The current in DC servo in a holding state can drop to zero if no feedback motion is sensed so they are basically off until either a command to feed is given or a rotation to resist is sensed by the encoder. The most prevalent difference is with the driver circuit. A straight DC motor driver must be tuned to the motor and its function for either holding current and/or running current and the associated chopper circuits in the drive or they 'sing' or over-current. That's not a problem with a stepper or AC servo motor since they are specifically designed for such applications.

I finally realized that I was over adjusting these Gecko 320's in a attempt to tune them. An oscilloscope with the diagram in the paperwork for the drive did the trick. That's when I began to realize that a stepper motor would be very well suited to do this job - no hassle.

Bill C.
Title: Re: What size motors?
Post by: Hood on April 20, 2009, 07:25:02 AM
Bill,
 excellent info, much appreciated, as they say, every day is a school day, shame I wasnt so interested in learning when I was there ;D

Hood
Title: Re: What size motors?
Post by: BClemens on April 20, 2009, 07:31:49 AM
 ;D
Title: Re: What size motors?
Post by: simpson36 on April 20, 2009, 09:37:34 AM
Bill, my sincere apologies if you felt demeaned in some way.

My comments were not directed at anyone in particular. I think some of the advice dispensed is not so much 'wrong' as it may be outdated, and out of context.

I don't think it is helpful to say steppers are 'just as good' as a blanket statement. Especially when it is obviously a newbee asking the question. Steppers are appropriate if used in such and such application, WHICH IS . . . ..  blah blah blah   BECAUASE . .  blah blah blah.  Mo' better answer.

There is a lot of conflcting information around and I know that as a newbee, I had trouble sifting thru it, primarily because AS a newbee, I had no tools to distiguish opinion from fact, or to dvine what information was missing from an answer.  I made some expensive mistakes following incomplete advice.  It cost me several hundreds of dollars to learn what an 'isolated signal' is, even though I had asked the right questions and purchased the exact components I was told to use. So, this being a forum, I share my 'experience' such as it is, like everyone else.

This is a technical forum. It's all about facts, not about personalities or one's "outlook on life".  :-*
Title: Re: What size motors?
Post by: BClemens on April 21, 2009, 05:20:55 AM
Trouble understanding what you read? Then blame the person attempting to help you. Expensive mistakes could be avoided if a basic understanding of basic electronics, basic mechanics, and a bit of humility are present. It's easy to see why you are in a predicament and can't seem to get out - you think everyone attempting to help is giving you wrong information and trying to steer you wrong. All that folks here will do is attempt to help you out with what they know to be true. The technical facts about a device are wasted on someone with little capacity to absorb it.

You ask vague questions and expect a purely technical , full of facts answer. What is a fact to you anyhow?

Bill C.

Hope to help....
Title: Re: What size motors?
Post by: simpson36 on April 21, 2009, 06:20:40 AM
Expensive mistakes could be avoided if a basic understanding of basic electronics, basic mechanics, and a bit of humility are present.

Bill, I don't know how I can be more humble than to admit that I do NOT have a basic understanding of electronics. I usually preceed any electronics question with exactly that statement. Sometimes you guys with all the valuable experience forget that and assume we newbees can fill in the blanks.

Speaking only for myself, I do a lot of homework and try to understand a topic at least in a rudimentary way before I ask questions, but I have no way to really fill in the blanks on an asnwer that I get on electronics issues, and somtimes that can cost us real money. I just wanted to point that out so that people (not just you personally) can keep that in mind.

i.e. it is better for an experienced person like yourself to over explain than to short sheet the answer assuming the questioner knows the rest.

I hope this clarifies my intent. You are free to disagree, but I really do not think I had anything bad to say about you as a person, so I dont understand your reaction here.
Title: Re: What size motors?
Post by: BClemens on April 21, 2009, 08:01:16 AM
Let's end this....I'm as much to blame....sorry for that!

I'm attempting to post a diagram for you....doesn't seem to work for some reason, but I've been able to in the recent past. I'll try again later.

Bill C.
Title: Re: What size motors?
Post by: NosmoKing on April 22, 2009, 03:34:29 PM
Just a comment on torque values for the respective technologies, Steppers, DC servo DCBL and AC servo generally all have maximum torque at zero speed, if you study their performance specs.
There have been many instances of machines being manufactured by high end users like  Mazak using Fanuc and Mits systems  using direct drive ball screws using DC servo's, agreed many of these were large motors, but torque is torque, whether stepper or servo.
On a similar note, Galil, which is one of the largest manufacturers of Motion cards do not appear to use steppers in any of  the dozens of application examples that they display on their web site, despite their cards being capable of step/dir.
Recently they won a face off for a very high speed, high precision positioning competition with Schneeburger mechanism.
http://www.galilmc.com/support/servotrends/st_10_08.pdf
Nosmo
 
Title: Re: What size motors?
Post by: MachineMaster on April 22, 2009, 04:01:42 PM
One thing that no one has mentioned is that with a stepper system if everything is ok it works but if anything goes wrong it stops.
A servo system on the other hand can fail in such a way that the servo takes off at full speed and goes until it hits something that can stop it.
That is the reason for the high cost of commercial servo controls. They have to be able to detect and stop any such failures.
Systems that only rely on the driver to recognize out of position moves don't have the safety of a system that also depends on the control.
Speed is not the most important thing when most of us are at best high end hobbyists. A mill that can move at 500 -600 IPM would scare a lot of us.
It is not as if shaving 30 seconds off of a part run would save us millions like it could in a major factory.
Title: Re: What size motors?
Post by: simpson36 on April 22, 2009, 05:32:14 PM
Torque over time = power. Power moves things, not torque.

The biggest difference, power wise, between steppers and servos is that the Stepper's torque drops off markedly with speed, whereas a servo does not. Also a stepper is rather severely speed limited. I just noted a document on the forum that shows a stepper loosing 75% of it's torque at high speed (high for a stepper).

Here is a comparison of the different motor types (when they are running) using Horsepower as the measure (universally understood).

HP = torque x speed / 5252

We start with equal torque stepper and servo, we'll be very conservative and say the stepper loses only half of the torqe and gets up to 1,000RPM (that would be a very good stepper)

Servo is not going to loose torque and will be running at 3,200 RPM (that would be an average servo)

Stepper 1.5625 ft-lbs * 1000 /5252 = .298HP

Servo    3.125   ft-lbs * 3200 /5252 = 1.904HP

Servo generates a bit more power. Those are the numbers.

As to the runaway issue with servos, in the case of the Gecko drive I am using, the drive provides the power to the motor, if somethign oges wrong, it simply faults and shuts down the motor. In the event the Gecko failed in some way that gave full juice to the motor, the setup can be wired in such a way that the limit switches shut down the current to the motors.

None of this means steppers are bad. It's just not a complete picture to simply compare a torque spec and draw the conclusion that the performance is anything near similar. 

It is what it is. Steppers are fine for some applications, but it is inaccurate to say that they are equal to servos in performance. My rig has steppers on three axis and they do just peachy for what I need. On the other hand, even a relatively large stepper was not up to the task of running my 4th axis, so I'm messing around with my forst servo motor now.













Title: Re: What size motors?
Post by: RHOLLIDAY on April 25, 2009, 12:21:27 AM
I just got my Sharp mill working on cnc. I used the Keling KL34H2120-60-4B  steppers 1200in.  Direct drive with Ruland couplings only 2 brackets for the x ,z and 3 for the y.
The Sharp is about a third larger than the Bridgeport. If you have ball screws I thank that the 1200in steppers would work just fine. I have not been able to find ball screws for the Sharp yet so am somewhat limited on max speed but it is much faster than hand cranking.  :)
Title: Re: What size motors?
Post by: simpson36 on April 26, 2009, 09:44:29 AM
I put ball screws on my mill as a prelude to the planned CNC conversion. I still cranked by hand, but 5 turns per inch was SOOOOO much better than 16 . . .  8)

It is not very difficult (famous last words) to make ball screws for any machine tool.
Title: Re: What size motors?
Post by: NosmoKing on April 26, 2009, 10:20:09 AM
It is not very difficult (famous last words) to make ball screws for any machine tool.

'If any machine tool' you mean manual machines as well, It has been my understanding that the main problem is back-feeding when the much lower friction B.S.'s are fitted?
Title: Re: What size motors?
Post by: simpson36 on April 26, 2009, 10:39:31 AM
That's an interesting point.

Certainly with a fast lead and ball tracks that would be the case. With a 5tpi el cheapo ball screw and a crappola asian mini mill like mine, not a problem. It took the effort from intellerable to bearable  :D